If in the future we end up needing a gnome2_src_test phase maybe would be safe to run them with GSETTINGS_BACKEND="memory", some ebuilds are already passing it and maybe it's one of the reasons of that bug reports (that are not 100% reproducible) of random dconf related errors due to missing schemas and similar. Also setting it to "memory" will ensure it don't get random settings from environment (as upstream needed to fix for example for libsoup at https://mail.gnome.org/archives/commits-list/2013-September/msg10555.html )
*** This bug has been marked as a duplicate of bug 511946 ***